Pole-piece for dynamo-electric machines.



A. CHURCHWARD. POLE PIECE FOR DYNAMIO ELECTRIC MACHINES. APPLICATION FILED AUG. 23, 1901.

907,738, Patented Dec. 29, 1908.

Fig.1.

W'Ltnesses. I nventor:

C fllexqnder hurchward.

UNITED STATES"PATENTOFFIGE; ALEXANDER CHURCH WARD, or CHICAGO, ILLINOIS, AssIeNon vTo"eEuER-lit Enter tis COMPANY, A CORPORATION or N W Yome; H z g p row-PIECE'FoaDYNAmo-ELEcTnIc MACHINES. j

Specification of Letters Patent. I Application am August 23, 1901. SeriaLRo. 73,056. 7

To all whom it may concern:

Be it known that I, ALEXANDER CHURCH- WARD, a citizen of the United States, residing at Chicago, county of Cook, State of Illinois,

have invented certain new and useful Improvements in Pole-Pieces for Dynamo- Electric Machines, of which the following is his invention relates to dynamo electric machines, and its-'object is to rovide a polepiece which will automatical y compensate or changes in load.

.Heretofore it has been the ractice to so design the pole-pieces that t e pole-tips,-

whether part of the pole itself or in the form .'of a shoe attached to said pole-piece, are

loads vary. For instance, i the brushes are I so set as to cause no sparking at no load, then when the heavy overloads come on, even if only momentarily, there will .be considerable sparking. On the other hand, if the brushes are set far enough forward to give a s arkless collection at full load or on the over oads, the machine will spark badly at no load.

My inventionaims to overcome all this trouble by so constructing the pole-pieces that the tips will be less saturated than the center of the pole-face, or in other words,

reversing the usual conditions of magnetization. Then, as the load increases and more flux is needed the shortest and easiest-path for the lines of force will be through the poletips, so that as the loadincreases, the reversing field will increase in proportionto the load. Moreover, in case a circuitbreaker opens on an overload, there will be no tendency for the machine to spark, as the flux which, the coil under the brush is cutting, Will be reduced the instant the circuitbreaker cuts ofi the current from the machine.

My invention isalso useful in rotary c'on- Patented Dec. 29, 1908, I

verters and in alternating current generators,

as it tends to keep the flux evenly distributed on the pole-face, which results in better regulation.

The'inven-tidritherefore consists in a polepiece having" a portion of its face removed at thef'ceritter in order to produce a higher degree'of saturation there than at the pole{ tips when the machine is running at no load or with a light load. This removal is most conveniently effected by cutting out the middle portion of the end of every other lamination, so that" the pole-piece will have a plurality of deep narrow parallel recesses extending in from the middle of the polcface, and preferably tapering from the outside inwards.

In the accompanying drawing, Figure 1 1s a side elevation of a multipolar ma hine,

showing also a longitudinal section of a pole piece embodying my invention, taken on a plane of rotation of a cooperating armature.

vFig. 2 is a longitudinal section of a single pole-piece in a plane at right angles to Fig. 1.

The poleiece is shown as built up of laminae a, w ich'may be provided with tips a, if-desired, either integral with the laminae, or in the form of a pole-shoe, as indicated by the dotted lines in Fig, 1. The laminae in the middle are'alternately cut away as shown in Fig. 1, the notch or recess a being preferably somcwhat tapering as shown.

The result is that the middle portion of the pole-face presents a smaller surfaceof metal to the armature than to the tips, so that the middle of the laminations become'sat'urat'ed before the pole-tips do, and thus any increase in the flux is forced to flow through the tips. This stifl'ens the field at the tips on an,1n-= crease of load, and avoids the necessity of any change in theposition of the brushes. The size of the notches a must be such as to properly proportion the, saturation of'the' two parts of the pole-piece to produce the right change in flux at the pole-tips as the load varies.

What I claim as new and desire to secure I chines composed of laminae, some of which by Letters Patent of the United States, isextend to the pole-face across thelr entire 1. A laminated pole-piece for dynamoi width, while the others extend thereto only 15- electric machines, having the middle portion at the tips, thereby increasing the magnetic 5 of alternate laminae cut away. reluctance at the middle of the pole-face.

2. A pole-piece for dynamo-electric ma- In witness whereof, I have hereunto set chines composed of laminae, a portion of my hand this 19th day of August, 1901. which are notched in the middle of one end to v ALEXANDER OHURGHWARD.

increase the magnetic reluctance at the mid- 10 dle of the poleface, the other laminae being Witnesses:

solid. BENJAMIN B. HULL,

3. A polepieee for dynamo-electrie ma- J. SORIBNER. 

